1). Field of the Invention
This invention relates to thin film magnetic heads, and in particular, to a method for fabricating narrow track width write heads comprising poles made of laminated pole-piece material and more particularly to a Ion beam Etch (IBE) process for trimming poles and to a specific material for the pole and write gate material that increases selectivity of the IBE.
2). Description of the Prior Art
Typical magnetic disk drives include a magnetic disk and a read-write head for recording data in and reading data from the disk. It has been a goal of industry to increase the recording density in magnetic disks. In order to achieve this goal, read-write heads have been developed comprising an inductive write element and a magnetoresistive read element. In addition, magnetic disks exhibiting high coercivity and low noise have been developed.
It is known in the art to use "pole-tip trimming" to reduce the write fringing field. (The fringing field is that portion of the magnetic field generated by the write element and extending toward tracks adjacent to the track being written to. It is important to minimize the write fringing field, especially when recording in disks having a high track density (i.e., disks recorded using a narrow pole width) because otherwise, the fringing field might partially erase or garble data in adjacent tracks.
At present, ion beam etching ("IBE") is the only proven high-volume etching technique for trimming deposited pole-piece layers into poles.
The use of IBE for patterned etching requires a mask to protect the portions of the read-write head that are not to be etched. The most common mask for IBE is photoresist. However, due to relatively low etch selectivity, thick photoresist is required for pole trimming. (Photoresist Etch selectivity refers to the ratio of the rate at which the pole-piece material is etched to the rate at which the photoresist is etched during IBE.) This limits the efficacy of using photoresist as a mask for trimming very narrow poles (e.g. poles with an aspect ratio greater than 2.0). Further, due to thick photoresist mask requirements, "redeposition" and "shadowing" become a severe problem when trimming narrow, high aspect ratio poles. After the photoresist mask is removed, "fencings" or "rabbit ears" remain above the pole-pieces. To minimize the "fencing" problem, a complicated, long ion-milling process, e.g. using multi-angle ion milling and a tedious post-milling photoresist stripping step, is used.
With regard to the magnetic read-write characteristics of a magnetic read-write head employed in reading and writing digitally encoded magnetic data from and into a magnetic data storage medium, it is known in the art of magnetic read-write head fabrication that increased track spacings of magnetic data tracks within magnetic data storage media are required when employing inductive magnetic write heads which exhibit increased write fringe fields bridging their magnetic transducer pole layers. Increased write fringe field widths within inductive magnetic write heads typically result from non-symmetric magnetic pole layers within those inductive magnetic write heads. A schematic cross-sectional diagram of a typical inductive magnetic write head formed with non-symmetric magnetic pole layers is illustrated in FIG. 1.
Shown in FIG. 1 is a substrate 10 having formed thereupon a lower magnetic pole layer 12 separated from an upper magnetic pole tip 16a within a patterned upper magnetic pole layer 16 by a gap filling dielectric layer 14. Also shown in FIG. 1 bridging from the lower magnetic pole layer 12 to the patterned upper magnetic pole layer 16 is a pair of write fringe fields 15a and 15b.
It is also known in the art of magnetic read-write head fabrication that write fringe fields, such as the write fringe fields 15a and 15b as illustrated in FIG. 1, formed incident to non-symmetric magnetic pole layer alignment within inductive magnetic write heads, may be significantly reduced by partially etching the wider of the two non-symmetric magnetic pole layers while employing the narrower of the two non-symmetric magnetic pole layers as a mask to form within the wider of the two non-symmetric magnetic pole layers a pole tip self-aligned with the pole tip within the narrower of the two non-symmetric magnetic pole layers. A schematic cross-sectional diagram illustrating the results of such partial etching practiced upon the lower magnetic pole layer 12 as illustrated in FIG. 1 is shown in FIG. 2.
Shown in FIG. 2 is a partially etched lower magnetic pole layer 12' having formed therein a lower magnetic pole tip 12a separated from the upper magnetic pole tip 16a within a partially etched patterned upper magnetic pole layer 16' by a patterned gap filling dielectric layer 14'. There is also shown in FIG. 2 bridging from the partially etched patterned upper magnetic pole layer 16' to the partially etched lower magnetic pole layer 12' a pair of significantly reduced write fringe fields 15a' and 15b'.
While the inductive magnetic write transducer structure as illustrated in FIG. 2 typically exhibits significantly reduced write fringe fields in comparison with the inductive magnetic write transducer structure as illustrated in FIG. 1, the inductive magnetic write transducer structure as illustrated in FIG. 2 is typically not formed entirely without difficulties. One of the difficulties typically encountered when forming the inductive magnetic write transducer structure as illustrated in FIG. 2 is that a substantial portion of the patterned upper magnetic pole layer 16' is eroded under circumstances where: (1) the lower magnetic pole layer 12 and the patterned upper magnetic pole layer 16 are both formed of a permalloy (ie: nickel-iron, 80:20 w/w) magnetic material, as is common in the art of magnetic read-write head fabrication, (2) the gap filling dielectric layer 14 is simultaneously formed of an aluminum oxide dielectric material, as is similarly common in the art of magnetic read-write head fabrication; and (3) the magnetic write transducer structure whose schematic cross-sectional diagram is illustrated in FIG. 2 is etched from the magnetic write transducer structure whose schematic cross-sectional diagram is illustrated in FIG. 1 through an ion beam etch (IBE) method employing argon ions, as is similarly also common in the art of magnetic read-write head fabrication.
The substantial portion of the patterned upper magnetic pole layer 16 is typically eroded due to an ion beam etch (IBE) selectivity of the ion beam etch (IBE) method for the patterned upper magnetic pole layer 16 with respect to the gap filling dielectric layer 14. Typically, using a N.sub.2 or Ar IBE, the ion beam etch selectivity of the patterned upper magnetic pole layer 16, when formed of a permalloy magnetic material, with respect to the gap filling dielectric layer 14, when formed of an aluminum oxide dielectric material, is from about 1:0.3 to about 1:0.6. That is the upper pole (16)Permalloy IBE rate is higher than the etch rate of the gap fill dielectric layer 14.
Problem 1: Erosion of the upper pole: Erosion of upper magnetic pole layers, such as the patterned upper magnetic pole layer 16, has been noted in the art of inductive magnetic read-write head fabrication, and it is typical in the art of inductive magnetic read-write head fabrication to compensate for the erosion by forming an upper magnetic pole layer with a substantial additional thicknesses beyond the thickness ultimately desired for a partially etched upper magnetic pole layer formed from the upper magnetic pole layer. See, for example, Krounbi et al., U.S. Pat. No. 5,438,747 (col. 11, line 68 to col. 12, line 5). Unfortunately, patterned upper magnetic pole layers, such as the patterned upper magnetic pole layer 16, formed with substantial additional thicknesses and thus significant aspect ratios, are often difficult to reproducibility form within magnetic transducer structures.
Although not specifically illustrated in FIG. 2, when fabricating a merged inductive write-magnetoresistive (MR) read magnetic head from the magnetic transducer structure whose schematic cross-sectional diagram is illustrated in FIG. 2, the partially etched lower magnetic pole layer 12' also serves as a top shield layer for a magnetoresistive (MR) sensor layer formed beneath the partially etched lower magnetic pole layer 12' within the merged inductive write-magnetoresistive (MR) read magnetic head. Under such circumstances, it is important that the partially etched lower magnetic pole layer 12' have sufficient remaining thicknesses at locations other than the location of the lower magnetic pole tip 12a in order to serve adequately as a top shield layer within the merged inductive write-magnetoresistive (MR) read magnetic head. While it is theoretically possible to assure adequate thicknesses of various portions of the partially etched lower magnetic pole layer 12' by increasing the thickness of the lower magnetic pole layer 12 from which is formed the partially etched lower magnetic pole layer 12', unfortunately, the thickness to which the lower magnetic pole layer 12 may be formed is itself often limited by design considerations when fabricating an inductive write-magnetoresistive (MR) read magnetic head.
Problem 2: Shadowing A related consideration pertinent to providing the partially etched lower magnetic pole layer 12' with sufficient thicknesses at locations other than the location of the lower magnetic pole tip 12a to serve adequately as a top shield layer for a magnetoresistive (MR) sensor layer fabricated beneath the partially etched lower magnetic pole layer 12' is that the etch rate of the partially etched lower magnetic pole layer 12' near the upper magnetic pole tip 16a within the partially etched patterned upper magnetic pole layer 16' is, as is illustrated in FIG. 2, reduced. The etch rate is reduced due to a shadowing effect inherent in the ion beam etch (IBE) method through which is conventionally formed the partially etched lower magnetic pole layer 12'. Due to the shadowing when the partially etched lower magnetic pole layer 12' is formed through the ion beam etch (IBE) method, there is formed as illustrated in FIG. 2 the lower magnetic pole tip 12a with a projection T.sub.2 with respect to immediately surrounding portions of the partially etched lower magnetic pole layer 12', while portions of the partially etched lower magnetic pole layer 12' further removed from the lower magnetic pole tip 12a are etched to remove a thickness T.sub.1 with respect to the lower magnetic pole layer 12, as illustrated in FIG. 2. In that regard, it is desirable within merged inductive write-magnetoresistive (MR) read magnetic head fabrication to provide partially etched lower magnetic pole layers, such as the partially etched lower magnetic pole layer 12', formed through etch methods which provide minimal shadowing, thus yielding partially etched lower magnetic pole layers where values of parameters which correspond with T.sub.1 and T.sub.2 are most closely approximate.
By way of example, if it is assumed that: (1) the etch rate of the material from which is formed the gap filling dielectric layer 14 as shown in FIG. 1 is equal to R.sub.gap ; (2) the etch rate of the material from which is formed the lower magnetic pole layer 12 as shown in FIG. 1 is equal to R.sub.1p ; (3) the gap thickness is equal to G as shown in FIG. 2; (4) the etch time is equal to t; and, (5) the convention ion beam etch (IBE) method shadowing effect provides an etch rate of the portion of the partially etched lower magnetic pole layer 12' most closely adjoining the partially etched patterned upper magnetic pole layer 16' one half the etch rate of the patterned lower magnetic pole layer 12' further removed from the partially etched patterned upper magnetic pole layer 16', as illustrated in FIG. 2, then the thicknesses T.sub.1 as illustrated in FIG. 2 is determined in accord with equation 1 and the thickness T.sub.2 as illustrated in FIG. 2 is determined in accord with equation 2. EQU T.sub.1 =(t-G/R.sub.gap)R..sub.1p (1) EQU T.sub.2 =(t-2G/R)R.sub.ip /2=nG (2)
Within equation 2, n typically varies from about 0.5 to about 3. Equation 3, equation 4 and equation 5 then follow from equation 1 and equation 2 EQU t=2nG/R.sub.1p +2G/R.sub.gap (3) EQU T.sub.1 =(2nG/R.sub.1p +G/R.sub.gap)R.sub.ip (4)
T.sub.1 /T.sub.2 =T.sub.1 /nG=2+R.sub.1p /nR.sub.gap (5)
Thus, it is seen from equation 5 that by selectively etching the material from which is formed the gap filling dielectric layer 14 with respect to the material from which is formed the lower magnetic inductor pole layer 12 within FIG. 1 there will be minimized the magnitude of T.sub.1 with respect to T.sub.2 as illustrated in FIG. 2.
A related difficulty encountered when forming from the patterned upper magnetic pole layer 16 whose schematic cross-sectional diagram is illustrated in FIG. 1 the partially etched patterned upper magnetic pole layer 16' whose schematic cross-sectional diagram is illustrated in FIG. 2 is illustrated by the schematic plan-view diagram of FIG. 3 and the schematic cross-sectional diagram of FIG. 4. The schematic plan-view diagram of FIG. 3 corresponds with the schematic cross-sectional diagram of FIG. 1. Shown in FIG. 3 is the gap filling dielectric layer 14 having formed thereupon the patterned upper magnetic pole layer 16, which in turn in part has formed thereupon a patterned photoresist layer 18 as is commonly employed to protect the coil region R2 of the patterned upper magnetic pole layer 16 when etching the pole tip region R1 of the patterned upper magnetic pole layer 16 to form the partially etched patterned upper magnetic pole layer 16'. Shown in FIG. 4 is a schematic cross-sectional diagram illustrating the results of etching the patterned upper magnetic pole layer 16 whose schematic plan-sectional diagram is illustrated in FIG. 3 to form the partially etched patterned upper magnetic pole layer 16'. The schematic cross-sectional diagram of FIG. 4 is obtained through the cross-sectional plan perpendicular to the cross-sectional plane employed in obtaining the schematic cross-sectional diagram of FIG. 2.
Shown in FIG. 4 is the partially etched lower magnetic pole layer 12' having formed thereupon the patterned gap filling dielectric layer 14' which in turn has formed thereupon or thereover: (1) a magnetic coil isolation dielectric layer 20 having formed therein a series of magnetic coils 22; (2) the partially etched patterned upper magnetic pole layer 16'; (3) and the patterned photoresist layer 18. As is illustrated in FIG. 4, the partially etched patterned upper magnetic pole layer 16' has a step 24 formed therein at the location of the patterned photoresist layer 18. The step 24 contributes to a significant step height H1 between the pole tip region R1 of the partially etched patterned upper magnetic pole layer 16' and the coil region R2 of the partially etched patterned upper magnetic pole layer 16'. Significant step heights within magnetic pole layers such as the partially etched patterned upper magnetic pole layer 16' are undesirable within the art of inductive magnetic read-write head fabrication since it is often difficult to accurately and reproducibly form upon those magnetic pole layers subsequent layers within the inductive magnetic read-write heads within which are formed those magnetic pole layers.
Various additional features of magnetic pole layer fabrication for use within inductive magnetic write heads have been disclosed by Krounbi et at. in U.S. Pat. No. 5,438,747, the teachings of which are incorporated herein fully by reference.
It is thus desirable to form within magnetic transducer structures which may be employed within inductive magnetic write heads self-aligned partially etched lower magnetic pole layers of permalloy alloy magnetic materials separated by patterned gap filling dielectric layers of aluminum oxide dielectric materials from partially etched patterned upper magnetic pole layers of permalloy alloy magnetic materials with minimal consumption of the partially etched patterned upper magnetic pole layers. It is also desirable to form within magnetic transducer structures which may be employed within inductive magnetic read-write heads partially etched patterned upper magnetic pole layers of enhanced flatness. Most desirable in the art are magnetic transducer structures which simultaneously possess the foregoing two characteristics. It is towards the foregoing goals the present invention is more specifically directed.
The importance of overcoming the various deficiencies noted above is evidenced by the extensive technological development directed to the subject, as documented by the relevant patent and technical literature. The closest and apparently more relevant technical developments in the patent literature can be gleaned by considering U.S. Pat. No. 5,438,747(Krounbi et al.) that teaches a pole trimming method. U.S. Pat. No. 5,867,890(Hsaia et al.) shows a RIE etch for pole tips. U.S. Pat. No. 5,726,841(Tong et al.) discloses a method for trimmed pole tips etched by Focused ion beam for undershoot reduction. U.S. Pat. No. 5,874,010(Tao et al.) shows a Pole trimming method using N.sub.2 ions. U.S. Pat. No. 5,878,481(Feng et al.) shows a pole trimming method for fabricating a magnetic transducer structure.